1. Field of the Invention
This invention relates to a time indicator and, in particular, to a time indicator wherein the relative amount of time that has elapsed from the initial activation of the indicator can be rapidly and easily determined by the progression of a visually perceptible change in color along different areas of the indicator. This invention also relates to a novel means for adjusting selected time periods for an indicator.
2. Prior Art
Numerous devices are known which provide a visual indication of the passage of a pre-arranged amount of time. Such time indicators are useful, for example, when attached to perishable items for indicating the length of time the items have been on the wholesaler's or retailer's shelf. Thus, foods and other perishable items such as photographic materials can be provided with indicators which evidence a visual change, after being activated and the passage of a predetermined period of time. Time-temperature indicators are also known which indicate a visual change as a function of both time and temperature Virtually any time indicator however is also, at least to a minor extent, dependent upon temperature.
It is highly desirable to have time indicators on automobiles in parking lots. Parking permits are normally printed cards or tags on which a parking attendant writes the appropriate times and dates. The tags are difficult to see from a distance, are easily duplicated or counterfeited, and a close examination of each tag by the attendant is impractical. To date, Applicants do not know of any commercially available vehicle parking permit which uses a chemical or physical-chemical means to indicate the status of the permit. The time indicators known in the art are problematic if used as parking permits in that the temperature of the interior of the car can vary dramatically from day-to-day and any time indicator, for example designed for a selected expiration time at room temperature, will not function effectively under conditions of use in an automobile. For example, with high temperatures (e.g., summer) the time indicator will indicate expiration earlier than desired and for low temperatures (e.g., winter) the time indicator will indicate expiration later than desired.
Applicant is aware of the following prior art, none of which teach or suggest the claims of this invention.
U.S. Pat. No. 3,018,611 to Biritz describes a time indicator device which may be used for frozen foods, parking times, construction periods, etc. The device comprises a backing which is attachable to the outer surface of, for example, a package of frozen food. Superimposed on the backing is a strip of filter paper having a chemical reagent laminated thereto. The chemical reagent is an oxygen reactive material The strip is hermetically sealed by a covering of transparent, impervious pressure sensitive cellophane which allows visual inspection of the oxygen reactive layer. A pin-hole size opening is provided in the covering to allow for ingress of air within the interior of the container This opening is sealed by a removable tape. When the tape is removed the oxygen reactive material reacts to change color by permitting air to enter and diffuse into the container to make contact with the material. The pin-hole opening is provided at one end of the container and as time proceeds, the color proceeds toward the other unexposed end of the container.
U.S. Pat. No. 3,520,124 to Myers, describes a parked car time indicator which includes a first sheet having a first reactant and a second sheet having a second reactant, and a release sheet, which is peeled away to permit contact of the first sheet with the second sheet to start a reaction over a selective time interval terminating with a color change of the reactants.
U.S. Pat. No. 3,480,402 to Jackson, describes a time indicator formed of an absorbent carrier having absorbed thereon at least one chemical compound which changes color upon exposure to oxygen. The carrier and chemical compound absorbed thereon are protected from ambient oxygen by a non-perforated barrier layer which is transparent and through which atmospheric oxygen can controllably diffuse over a preselected period of time. Thus, when the chemical compound changes color, the preselected period of time is indicated. The graduated time indicator may be produced by utilizing more than one chemical or a layer covering the various pieces of absorbent material of different thickness. For each piece of absorbent material, the chemical absorbed on the piece of absorbent material would change color at different times, e.g., the chemical on one piece would change color after, say, one week, and the chemical absorbed on another piece would change color after ten days, and the chemical on a further piece of absorbent material would change color after fourteen days. Thus, a graduated time indicator is described.
U.S. Pat. Nos. 3,954,011 and 3,962,920 to Manske, describes a time indicating device suitable for visibly measuring parameters such as time, temperature and time-temperature relationships. The device includes a porous fluid-carrying pad, a wick material for said fluid and an indicator means whereby the progress of fluid along the wick material can be visibly indicated and used to measure the passage of time, the exposure to a given minimum temperature or time-temperature relationship.
U.S. Pat. No. 4,028,876 to Delatorre describes an apparatus for visually indicating elapsed time by a color change which comprises a transparent container having a rupturable capsule therein and in which a first composition is contained A transparent matrix surrounds the second composition which is also in the container. The device may be secured to a surface by means of a mechanical fastener or an adhesive layer.
U.S. Pat. No. 4,212,153 to Kydonieus, et al describes a laminated indicator which changes in a visually perceptible mode with the passage of time. The indicator comprises at least two layers whereby the molecular migration of an agent in an interior layer to the outermost surface of the exterior layer causes a change which is visually perceptible. This reference also describes the use of a step-wedge test color panel placed next to the indicator which is used to compare the developed color or shade. The step-wedge can be provided with indicia corresponding to the time period required to develop the color at each step of the wedge.
Attention is also drawn to U.S. Ser. No. 07/401,080 entitled "Time Indicator Enhancement Method", filed Aug. 31, 1989, and now U.S. Pat. No. 4,903,254, which is an improvement of the aforementioned Kydonieus, et al. patent, U.S. Pat. No. 4,212,153 in that it provides a time indicator badge which provides a clear indication of the expiration of time.
U.S. Pat. No. 4,229,813 to Lilly, et al describes a time indicator which utilizes a silicon oil which is slowly absorbed onto and moves up a porous strip at a rate which is a function of time. One side of the strip is printed with an oil soluble ink, while the other side is unprinted. The printed side of the strip is laminated with polyethylene film to an unprinted strip. As the silicon oil moves up the strip, the oil contacts the ink causing a dye in the ink to migrate from the printed side to the unprinted side, thus providing a measurable color front moving up the strip.
U.S. Pat. No. 4,382,700 to Youngren describes an indicator which contains a mineral jelly which is in contact with a wick, such that the mineral jelly diffuses into the paper in accordance with the changes in ambient temperature over a period of time.
U.S. Pat. No. 4,408,557 to Bradley, et al describes a timer comprising an absorptive layer disposed on a base layer which accepts a carrier mixture at a predetermined rate. A barrier means is disposed between the carrier mixture and the absorptive layer, and the removal of the barrier activates the timer.
U.S. Pat. No. 4,629,330 to Nichols describes a color change indicator which includes a liquid having a predetermined index of refraction and a rate of evaporation, a reservoir for holding liquid, and an opacifying layer of microporous material. The opacifying layer has an index of refraction approximately the same as that of a liquid and overlies the reservoir. The opacifying layer has an open cell network of pores for absorbing liquid from the reservoir and is in a first radiation scattering condition when the liquid occupies the opacifying layer, and in a second scattering condition when the liquid is depleted from the opacifying layer.
U.S. Pat. No. 4,643,122 to Seybold describes a diffusion controlled security tag comprising a carrier containing a solution of a compound which changes color upon diffusion or evaporation of the solvent. The carrier is enveloped in a barrier film which controls the rate of diffusion/evaporation of the solvent from the carrier, such that a change in color of the carrier indicates undesirable storage or product tampering.
One of the problems associated with all of the foregoing devices is that they are complicated to adjust for a selected period of time. This often involves experimentation with many types of inks, solvents, wicks, etc. to prepare a device which can operate under the conditions expected. Additionally, very few of these devices can indicate the relative length of time that has elapsed since the device was activated, i.e., it is difficult to determine what fraction of the selected period of time has elapsed. Most of the prior art devices gradually change color over a period of time and involve, at best, a guess on how much time has elapsed. When this is combined with the possible variations in temperature, humidity, etc. that may exist in the environment of the time indicator, the viewer has very little confidence that he is close to the expiration time of the device.
A need thus exists for a timer which is inexpensive and can clearly, relatively accurately and quickly indicate the lapse of progressive selected periods of time increments. Further, there is a need for a means for easily adjusting the selected period of time without the cumbersome trial and error methods used in the past.